Fans can be seen behind Willian as he opens the scoring in HungaryCredit: Reuters

“Any individuals that can’t summon the brainpower to comprehend this simple message, and are found to have shamed the club by used using anti-Semitic or racist words or actions, will face the strongest possible action.”

Chelsea fans singing the song were shopped by outraged fellow supporters, who took to social media to expose the latest incident of racist behaviour to stain the club’s reputation.

Police are investigating last Saturday’s incident at Stamford Bridge as a possible hate crime. Two men have come forward, but deny using racist language.

Chelsea will attempt to find anyone involved in singing anti-Semitic songs last night.